Traditional base plated posts used in a guardrail system are manufactured from relatively strong rigid materials such as steel. Despite the posts being relatively strong in their own right the strength of the system is typically relatively weak as its capacity is limited by the pullout resistance of anchor bolts that secure the base plated posts to the underlying ground/concrete slab. Rigid post systems absorb the full force of the impact with little deflection resulting in a high peak load being transferred to the anchor bolts.
To maximize load carrying capacity, a rigid post system would require a base plate with a large footprint effectively enabling the anchor bolts to be positioned as far as possible from the base of the post on the impact side of the post. The further the bolts are distanced from the base of the post the lower the pullout force experienced by the anchor bolts during collision with the system.
However, larger plates may be difficult to accommodate in a car park environment. Moreover, despite a design that may position the anchor bolts at a reasonable distance from the bottom of the post, rigid post systems typically require numerous anchor bolts in order to have sufficient capacity to resist the impacting vehicle on the system.
The material costs of large base plates can be prohibitive and holes drilled for multiple fastening bolts may compromise the structural integrity of an underlying concrete slab, which could be of particular concern if the slab forms an elevated floor in a multi-level car park.